p. H. SCHOl'TE. -Tiie seclioii of llie ineasiirc-|Milyl(ipe .1/,, ot space Sp,, willi a ceiilial span 

 Sp„-i perpendicular lo a iliagoiial." 



b c '^ d 



72 = 4- 



/ 5 10 , 10 5 1 



/I = 6 



Proceedings Boyal Acad. Amsterdam. Vol. X. 



/ 7 Zl 35 . 35 Z1 y ƒ 



-4^- 



/fe^ 



^ e—T' 



'M±- 



m=. 



XI 



'^ 



1 8 Zg 56 70 56 >Z.8 



8 



71 = 8 



